dullen vs etiolate

dullen

verb
  • To become dull or duller; to dull. 

  • To make dull or duller; to dull. 

etiolate

verb
  • To become pale or blanched. 

  • To make pale through lack of light, especially of a plant. 

  • To make pale and sickly-looking. 

adj
  • etiolated 

How often have the words dullen and etiolate occurred in a corpus of books? (source: Google Ngram Viewer )